One particular form of such a chip cutting tool is of the ball-nose type and comprises a tool holder having an insert retaining pocket and a curing insert replaceably mounted and clamped therein. With such a tool, the feed movements of the tool and/or of the workpiece with respect to each. other arc multidirectional and this, taken together with the curved cutting edge of the insert, gives rise to relatively great cutting force components acting on the insert in general and on the cutting edge in particular. In consequence, the design of the cutting insert, its positioning on and mode of clamping to the tool holder, as well as the design of the retaining pocket, have to be such that these forces do not give rise to damage of the cutting insert and/or its retaining pocket or weaken the secure clamping and positioning of the insert in the pocket whilst, at the same time, allowing for efficient machining.
U.S. Pat. No. 4,512,689 discloses a typical chip cutting tool of this kind. The cutting tool comprises a disk-shaped cutting insert having indexable cutting edges and mounted in an insert retaining pocket of a tool holder by means of a clamping screw so that one of the cutting edges projects out of the pocket constituting thereby an operative cutting edge and at least one other cutting edge being located inside the pocket and constituting an inoperative cutting edge. To ensure secure fixing of the insert in the pocket a base and portions of rear side walls of the insert are adapted to abut respectively a base and side walls of the pocket.
However, this prior disclosure does not deal with problems which arise with tools having relatively small cutting diameters, e.g. about 10 mm or less. These problems involve achieving miniaturization of the tool whilst providing an adequate space for chip forming and evacuation, and all that without decreasing a cross-sectional dimension of the tool body and affecting the strength of the insert and the clamping screw.
It is the object of the present invention to provide a new and improved chip cutting tool, particularly for contouring of shaped surfaces requiring small cutting diameters, where the above problems are effectively solved.